Tabs are in general use for the removal of peelable panels and typically are formed from a projection of the panel. By grasping the tab, the panel can be peeled off a container. The material of the peelable panel and integral tab typically comprises a laminate structure, which may include a heat sealable layer and a barrier layer such as aluminium and/or varnish. In closures on containers for food products which require processing by retorting, for example, the tab may be folded over the main part of the panel in order to avoid handling problems. Often the peelable panel is fixed to a metal ring which is then seamed to the edge of a can body. In order to avoid damage to the tab, particularly during processing, it is usual to fold the tab radially inwardly away from the ring prior to the seaming operation.
Folding the tab of a peelable panel which includes a thick layer of aluminium can be carried out in a relatively straightforward manner by using the material's inherent deadfold properties. A typical folding process for such a tab/panel is carried out in three steps as shown in FIG. 1. Firstly the peelable panel 1 is fixed to a metal ring 2 by heat sealing (FIG. 1(a)). The ring 2 includes a flat annulus 3, an upright wall 4 and a seaming panel 5. During heat sealing, the tab 6 is forced by the heat sealing tool 10 around the wall 4 at the side of the ring so as to lie in a position approximately perpendicular to the centre part of the peelable panel. In a second operation, a folding tool 11 passes laterally over the seaming panel (FIG. 1(b)) until it contacts the tab and folds the tab 6 over the annulus 3 of the ring 2 and main part of panel 1 (FIG. 1(c)). When the tool 11 is removed, deadfold in the tab/panel material maintains the tab 6 in its folded position (FIG. 1(d)). Finally, a press tool 12 crushes the tab flat against the rest of the peelable panel 1 (FIG. 1 (e)).
This prior art folding method is only suitable for material which has inherent deadfold properties, typically including an aluminium layer of around 70 μm (microns) in thickness. In all types and thicknesses of lidding material, the tab has to stay on, or very close to the lid panel to avoid being damaged during handling and/or seaming. With flexible material structures, the lidding may be a three or four layer structure using less than 30 μm (microns) or at most 40 microns of aluminium, typically 0 to 10 μm. Not only would the tab crush operation of FIG. 1(e) fail to maintain the tab of such flexible lidding structures in the desired folded position, but flexible tab material adjacent the upright wall and seaming panel of the ring 2 is free to move and tends to wrinkle or to develop a fold in a non-ideal position during the folding and “crushing” operations (FIGS. 1(d) and (e)), thus risking damage to the tab.
This invention seeks to provide a method and apparatus for use with ends in which the tab and lid structure are formed from the same flexible material, which has no inherent deadfold characteristic.